Heavy duty line tightener



FIG. 1 is a front elevational view of the heavy duty line tightener of my invention;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a side elevational view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof.

The opposite side view is a mirror image of FIG. 3. 

The ornamental design for a heavy duty line tightener, as shown and described. 